1. Field of the Invention
The present invention relates to a canned motor having casings made of sheet metal such as stainless steel or the like and a pump employing such a canned motor, and more particularly to a canned motor having a welded structure which lends itself to a wide variety of pump designs and a pump employing such a canned motor.
2. Description of the Prior Art
There have heretofore been full-circumferential flow pumps designed for cooling the motor and reducing noise from the motor. Strong demands for pumps of non-seal structure which do not have sealing devices such as mechanical seals or the like are met by canned motor pumps and magnet drive pumps. The greatest requirement which present pumps have to meet is a reduction in size. One effort to meet the requirement is directed to increase the rotational speed of the motor with a frequency converter such as an invertor or the like. It has been customary to protect pumps from corrosive water by encasing the pump with a housing made of pressed corrosion-resistant stainless sheet.
Generally, pumps can be classified into different structures including multistage pumps and double-suction pumps by performance limitations, and also classified into ground-installed pumps and submerged pumps by limitations on the environment in which they are used.
Four main requirements to be met by pumps are thus summarized as (1) silence, (2) small size, (3) non-sealed structure, and (4) corrosion resistance. However, actual technical limitations have prevented pumps which satisfy all the four requirements from being produced so far. Accordingly, manufacturers have been required to produce a wide variety of pumps. Conventional full-circumferential flow pumps have also been categorized into different structures, and it has been necessary for manufacturers to produce full-circumferential flow pumps of different structures though they have the same output power. Such a conventional practice has been poor in productivity.